Receiver Troubleshooting

General discussion and support for the Peaberry SDR V1.

Receiver Troubleshooting

Postby kb3vuk » Thu Dec 27, 2012 2:28 am

Receiver Troubleshooting

So I'm not to sure how to proceed, spent the better part of today going over my work. So far I have completed the receiver section and most of the transmitter section. At each point I try to test my work so that any fault would be easier to fix. So far I am unable to receive anything other then static when using both PowerSDR or HDSDR ( I wanted to rule out software ).

Steps taken/observations:

1) go over all solder joints, %99.9 sure connections are good
2) traced signal from the antenna through Q1 and into the primary of T2 using a 3.5mhz test signal, as far as I can tell signal is making it to T2 and hopefully into R50 and R510
3) Q2 is off as I imagine it should be
4) Tried to tune WWV on all frequencies, unable to receive
5) measured voltage @ R50, R51, and C10, shows 2.5volts
6) in moving the scope probe to input pins on U6 would cause the static to die for a moment and then return. sometimes the SDR would reset and I would have to relaunch the software
7) moving the probe between R50 and R51 would cause a noticeable change in output, would seem the op-amp down stream is getting signal and processing it
8) could it be T2??

Any suggestions?

Thanks!
kb3vuk
 
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Re: Receiver Troubleshooting

Postby AE9RB » Thu Dec 27, 2012 3:50 am

What band set did you build? I'll assume it's one that should pass 3.5MHz. Why did you stop tracing the signal at T2? You should see it all the way to U6. If you tune to 3.51MHz then you should see 10kHz all the way from U6 to U10.
73 David AE9RB
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Re: Receiver Troubleshooting

Postby kb3vuk » Thu Dec 27, 2012 5:36 am

- 40/30/20
- 3.5Mhz was as high as my bench top function generator would go, I have since repeated the test with an RF generator @ 10Mhz. It looks like the input network will only pass a sine wave unmolested from about 5Mhz to 11Mhz, so 3.5 would not have made it though anyway ( input of U6 ). Anything above or below that and the waveform is attenuated/garbage, so maybe not quite getting to 20 meters?
- When leaving U6 and going to U5, via Pin 7&9, I see 2.5V DC offset with what looks like my signal at about 50mVp-p AC, sweeping the input frequency has no noticeable affect
- From U5 to U10 by pin 1 and 7, I see my signal again - the waveform is all jagged and my meter bounces around 3-4Mhz, probably not accurate
- I tuned the radio to 10khz off of what my signal generator was putting out and I see no change from the constant noise, is it possible that tuning is not happening? definitely not seeing the 10khz you mentioned
- Yes I can trace a reference signal from the antenna to U10 ( this has been a pretty awesome learning experience ) - bed time....
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Re: Receiver Troubleshooting

Postby AE9RB » Thu Dec 27, 2012 5:56 am

3.5MHz will not be usable for testing a 40/30/20 radio, but 10MHz is good. You mention some voltage levels but never told me what your signal generator is set for so I can't tell you if they are correct or not. Maybe QSD_0 and QSD_1 don't have a signal from the Si570.
73 David AE9RB
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Re: Receiver Troubleshooting

Postby kb3vuk » Thu Dec 27, 2012 5:19 pm

From the top:

Test signal: 10.03Mhz sine @ 1V p to p
Scope probe set to 10x

- With Power off
- C7, 10Mhz @ 1V p to p with 180 degree phase shift

- With Power on
- Measured test signal is now 750mV p to p
- C7, 10Mhz @ 750mV with 180 phase shift
- C9, 10Mhz @ 750mV, same phase shift
- C10 - 2.5V ( reference point for T1 )
- R50, 2.5v DC offset with about 350mV p to p AC wave, still 180 out of phase with reference signal
- R51, 2.5vDC with about 350mV AC signal - now back in phase with input ( is this right? )

- QSD_0 measured to be 14.08Mhz with a frequency counter
- QSD_1 again 14.08Mhz
- with a scope I see a 7.5V p to p waveform on QSD_1 ( I have a DSO-2090 so I'm not sure if I can trust the scope at these freqs ) with bandwidth limit off ( 20ns horizontal ) I see 12V p-p
- Using a DC voltmeter I see 2.5V on each input

- VINL - 2.5v DC, AC waveform observed about 4Mhz @ 50mV p-p
- VINR - 2.5v DC, same waveform as above
- power off reference signal and the waveform dies…. we're making it this far

U9 Si570
- pin 4, 56.3198Mhz at about 500mV p-p ( this is the upper end of my scope's capability i think )
- Test procedures for the I2C connection?
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Re: Receiver Troubleshooting

Postby AE9RB » Thu Dec 27, 2012 5:51 pm

Everything looks good up to U6. The signal is gone at VIN. Measure the input to U5 (output of U6).
73 David AE9RB
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Re: Receiver Troubleshooting

Postby kb3vuk » Thu Dec 27, 2012 8:07 pm

U6 to U5 Inspection

- Node 1A and 2A measured at R9 (2.512V) and R8 (2.511V) ( DC meter )
- No decrenable AC waveform on the scope, noise spikes?
- Checked pins 7 and 9 directly, compared to what the input looks like ( DC offset AC wave form ), I don't see a signal coming out

- Reviewed block diagram and 3253 data sheet
- OE1 and OE2 read low ( as they should )
- Checked S0 and S1, both are mostly 180 out of phase
- Should the frequency of QSD change as the radio is tuned in software? How do I know that the SW is actually having a change in HW?
- Could U6 be damaged
- What should I expect out of U6? The IF?
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Re: Receiver Troubleshooting

Postby AE9RB » Thu Dec 27, 2012 10:35 pm

I just noticed that you're not changing the LO frequency. 14.08 is the default. Try using this program:

http://pe0fko.nl/CFGSR/

1A and 2A aren't DC. You should see signal there. U6 is a mixer in this application.
73 David AE9RB
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Re: Receiver Troubleshooting

Postby kb3vuk » Fri Dec 28, 2012 12:42 pm

Just turn it on they said!! Kind of feel like the guy that forgot to plug it in - although I know more about receiver circuits then before. I used the config app to change to LO ( and here I thought that HDSDR and PowerSDR controls actually DID something ). Found the Exit_IO stuff and got HDSDR working with the hardware. Consequently signal passed to U5 and it looks like we have a living, breathing receiver. I was able to receive a few tones but still no WWV, I suspect the next hurdle will be to get some more height on the antenna. While I can get 2M/10M in the apartment, 40/30/20 may be asking a bit much.

Thanks for your help
kb3vuk
 
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Re: Receiver Troubleshooting

Postby rw6hch » Fri Dec 28, 2012 2:51 pm

for KB9VUK
Do you have a program CFGSR V2.5?
Really need to get to work HDSDR transmitting.
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